The continuous increase in the speed and in the frequency of train traffic brings about conditions that are increasingly rigid regarding maintaining the quality of the roadbed.
A good roadbed is the first condition of this quality since the economy, the comfort and the safety of the trains depend on it.
Periodic filling of the roadbed sleepers, straightening and levelling of the track, tightening of the rail fasteners to a large extent contribute to the maintenance of the roadbed, but these operations are not completely sufficient to ensure this maintenance because the stresses developed by the rolling equipment subject the head of the rails to very severe wear which causes its deformation.
This deformation, to which both the longitudinal and transverse profiles of the head of the rails are subjected, spreads over the rail tread and its bead and it has the effect of creating vibrations and impact which reach both the rolling equipment and the roadbed. As a result, fatigue of the rolling equipment is increased and, in turn, destruction of the track and its roadbed is accelerated. Furthermore, the vibrations and impact resulting from this deformation produce noise which adversely affects the comfort of the travelers and of people in the vicinity of the roadbed.
It is, therefore, also necessary for the maintenance of railways to periodically true the worn out and deformed surfaces of the head of the rails to retain its rolling quality in order to avoid the above-mentioned disadvantages.
Processes are already known for the truing of the worn surfaces of the heads of rails which comprise displacing, at generally constant speed along the generatrics of such surfaces, a predetermined number of grinding tools angularly oriented in a plane perpendicular to the rail and each operating along a tangent to the transverse profile of the rails, in such a manner as to obtain, after a certain number of cuts, a head which is trued according to an outline which is as close as possible to the ideal profile, at least in its working portions; the tread, the bead and the inner face of the rail.
This arrangement of the grinding tools, at different inclinations according to their position about the rail head, causes the component of their own weight which is perpendicular to their working tangent, to vary from one position to the other and the result of this condition is to proportionally increase or decrease the bearing force which is applied on such tools. Furthermore, for the same bearing force, the cutting depth of the grinders is not the same according to the orientation of the working tangent which may contact the profile of the head over surfaces that are more or less extensive, depending on the radius of curvature of such surfaces. Thus, a grinding tool operating tangentially over the tread, which is almost flat, penetrates into the metal less than a tool working tangentially over the head, which is round. Finally, it must also be considered that depending on the shape of the track, from straight stretches to small radius curves, the areas of maximum wear of the head of the rails are not the same and it is sometimes the tread and sometimes the bead that are most damaged.
All these considerations sometimes make it necessary to adjust the bearing pressure of the grinding tools for each position of the latter about the profile of the head of the rails to follow the prescribed shape of its profile. It is also necessary to adjust the bearing pressure of all the grinding tools of a stretch of rails differently from that of all the grinding tools of another stretch in the case, for instance, of curves where the inner stretch is more often affected by the rolling material.
All these adjustments are presently carried out manually by operators and the quality of the adjusted grinding operation depends exclusively on the skill and the experience of such operators. In view of the large number and complexity of such adjustments, it can easily be understood that they give rise to difficult problems.